Agroecological Advantages of Early-Sown Winter Wheat in Semi-Arid Environments: A Comparative Case Study From Southern Australia and Pacific Northwest United States.

David J Cann,Felicity A J Harris,Kenton D Porker,William F Schillinger,James R Hunt

doi:10.3389/fpls.2020.00568

Abstract

Wheat (Triticum aestivum L.) is the most widely-grown crop in the Mediterranean semi-arid (150–400 mm) cropping zones of both southern Australia and the inland Pacific Northwest (PNW) of the United States of America (United States). Low precipitation, low winter temperatures and heat and drought conditions during late spring and summer limit wheat yields in both regions. Due to rising temperatures, reduced autumn rainfall and increased frost risk in southern Australia since 1990, cropping conditions in these two environments have grown increasingly similar. This presents the opportunity for southern Australian growers to learn from the experiences of their PNW counterparts. Wheat cultivars with an obligate vernalization requirement (winter wheat), are an integral part of semi-arid PNW cropping systems, but in Australia are most frequently grown in cool or cold temperate cropping zones that receive high rainfall (>500 mm p.a.). It has recently been shown that early-sown winter wheat cultivars can increase water-limited potential yield in semi-arid southern Australia, in the face of decreasing autumn rainfall. Despite this research, there has to date been little breeding effort invested in winter wheat for growers in semi-arid southern Australia, and agronomic research into the management of early-sown winter wheat has only occurred in recent years. This paper explores the current and emerging environmental constraints of cropping in semi-arid southern Australia and, using the genotype × management strategies developed over 120 years of winter wheat agronomy in the PNW, highlights the potential advantages early-sown winter wheat offers growers in low-rainfall environments. The increased biomass, stable flowering time and late-summer establishment opportunities offered by winter wheat genotypes ensure they achieve higher yields in the PNW compared to later-sown spring wheat. Traits that make winter wheat advantageous in the PNW may also contribute to increased yield when grown in semi-arid southern Australia. This paper investigates which specific traits present in winter wheat genotypes give them an advantage in semi-arid cropping environments, which management practices best exploit this advantage, and what potential improvements can be made to cultivars for semi-arid southern Australia based on the history of winter wheat crop growth in the semi-arid Pacific Northwest.

Highlights

The cropping systems of Mediterranean semi-arid southern Australia are diverse, resilient and responsive to change
This paper argues that differences exist between the environmental conditions and production systems of the two regions, there is a benefit in applying some of the genotype × management synergies that have been successful in the low-rainfall regions of the Pacific Northwest (PNW) to wheat production in semi-arid southern Australia
If fall rains do not arrive until late November, grain yield potential of late-sown winter wheat will likely be reduced by 50% or more compared with early-sown winter wheat (Schillinger, 2016)

Summary

Introduction

The cropping systems of Mediterranean semi-arid southern Australia are diverse, resilient and responsive to change. Within a context of rising business costs and increased income risk these effects have already been visible across southern Australia since 1990, decreasing water-limited potential wheat yield (PYW) and increasing the difficulty of establishing crops during autumn, the traditional sowing period for spring wheat (Pook et al, 2009; Hochman et al, 2017). A resilient response to the challenges of a changing environment is unlikely to be achieved through a singular technical or genetic development. Historic increases in Australian wheat yields have not been the result of individual advancements in crop genotype or crop management, but instead when the combination of crop genotype, environment and management has created synergies through which yield is increased more than can be accounted for through each development alone (Kirkegaard and Hunt, 2010; Hunt et al, 2019a)

Methods

Findings

Conclusion